- Glasgow-haskell-users

Explicit calls to the garbage collector.
by Jurriaan Hage 08 May '12

08 May '12

LS. I have a very memory intensive application. It seems that the timing of my application depend very much on the precise setting of -H...M in the runtime system (-H2000M seems to work best, computation time becomes a third of what I get when I pass no -H option). I conjecture that this good behaviour is the result of gc happening at the right time. So I wondered: if I can one when is the right time, is it possible then to trigger GC explicitly from within the Haskell code? best, Jur

5 5

Weird behavior of the NonTermination exception
by Bas van Dijk 04 May '12

04 May '12

Hello, Before I turn the following into a ticket I want to ask if I miss something obvious: When I run the following program: ------------------------------------------------- import Prelude hiding (catch) import Control.Exception import Control.Concurrent main :: IO () main = do mv <- newEmptyMVar _ <- forkIO $ do catch action (\e -> putStrLn $ "I solved the Halting Problem: " ++ show (e :: SomeException)) putStrLn "putting MVar..." putMVar mv () putStrLn "putted MVar" takeMVar mv action :: IO () action = let x = x in x ------------------------------------------------- I get the output: $ ghc --make Loop.hs -o loop -O2 -fforce-recomp && ./loop [1 of 1] Compiling Main ( Loop.hs, Loop.o ) Linking loop ... loop: thread blocked indefinitely in an MVar operation I solved the Halting Problem: <<loop>> putting MVar... putted MVar As can be seen, the putMVar is executed successfully. So why do I get the message: "thread blocked indefinitely in an MVar operation"? Note that if I change the action to a normal error the message disappears. I discovered this bug when hunting for another one. I have a Haskell web-server where one of the request handlers contained a loop. All exceptions thrown by handlers are caught and logged. When executing the looping handler I noticed ~0% CPU usage so I assumed that the handler wasn't actually looping because a NonTermination exception was thrown. However for some reason the NonTermination exception was not caught and logged. I haven't yet isolated this bug into a small test-case but when trying that I discovered the above. Regards, Bas

3 5

trouble building ghc-7.4 on Fedora 18 (devel) ARM
by Jens Petersen 04 May '12

04 May '12

Hi, I have been struggling to build ghc74 on ARM (ideally with llvm3) on Fedora 18 (the current development tree). After applying 4 recent ARM patches from Debian the ghc-7.4.1 build gets to: : "inplace/bin/ghc-stage1" -H32m -O -package-name base-4.5.0.0 -hide-all-packages -i -ilibraries/base/. -ilibraries/base/dist-install/build -ilibraries/base/dist-install/build/autogen -Ilibraries/base/dist-install/build -Ilibraries/base/dist-install/build/autogen -Ilibraries/base/include -optP-DOPTIMISE_INTEGER_GCD_LCM -optP-include -optPlibraries/base/dist-install/build/autogen/cabal_macros.h -package ghc-prim-0.2.0.0 -package integer-gmp-0.4.0.0 -package rts-1.0 -package-name base -XHaskell98 -XCPP -O2 -no-user-package-conf -rtsopts -odir libraries/base/dist-install/build -hidir libraries/base/dist-install/build -stubdir libraries/base/dist-install/build -hisuf hi -osuf o -hcsuf hc -c libraries/base/dist-install/build/GHC/Event/Clock.hs -o libraries/base/dist-install/build/GHC/Event/Clock.o [parallel build line removed] /usr/bin/ld: error: /tmp/ghc5703_0/ghc5703_0.o uses VFP register arguments, libraries/base/dist-install/build/GHC/Event/Clock.o does not /usr/bin/ld: failed to merge target specific data of file /tmp/ghc5703_0/ghc5703_0.o collect2: error: ld returned 1 exit status make[1]: *** [libraries/base/dist-install/build/GHC/Event/Clock.o] Error 1 (full build log at: http://arm.koji.fedoraproject.org/koji/getfile?taskID=723311&name=build.log and more details at http://arm.koji.fedoraproject.org/koji/taskinfo?taskID=723311) I gather that it builds on Debian so I am not quite why it is failing on Fedora. To see if ghc-7.4.2pre is any better I tried building ghc-7.4.1.20120416 too (without any ARM patches), which gets a lot further, to using llvm: "inplace/bin/ghc-stage1" -H32m -O -package-name array-0.4.0.0 -hide-all-packages -i -ilibraries/array/. -ilibraries/array/dist-install/build -ilibraries/array/dist-install/build/autogen -Ilibraries/array/dist-install/build -Ilibraries/array/dist-install/build/autogen -Ilibraries/array/include -optP-include -optPlibraries/array/dist-install/build/autogen/cabal_macros.h -package base-4.5.1.0 -XHaskell98 -XMultiParamTypeClasses -XFlexibleContexts -XFlexibleInstances -XTypeSynonymInstances -XDeriveDataTypeable -XStandaloneDeriving -XRank2Types -XMagicHash -XUnboxedTuples -XForeignFunctionInterface -XUnliftedFFITypes -XCPP -O2 -no-user-package-conf -rtsopts -odir libraries/array/dist-install/build -hidir libraries/array/dist-install/build -stubdir libraries/array/dist-install/build -hisuf hi -osuf o -hcsuf hc -c libraries/array/./Data/Array/IO/Internals.hs -o libraries/array/dist-install/build/Data/Array/IO/Internals.o libraries/array/Data/Array/IO/Internals.hs:2:16: Warning: -#include and INCLUDE pragmas are deprecated: They no longer have any effect Instruction referencing instruction not embedded in a basic block! %ln2ulc = getelementptr inbounds i32* %Sp_Arg, i32 3 %ln2uld = ptrtoint i32* %ln2ulc to i32 Instruction does not dominate all uses! %ln2ulc = getelementptr inbounds i32* %Sp_Arg, i32 3 tail call cc10 void @stg_ap_ppp_fast(i32* %Base_Arg, i32* %ln2ulc, i32* %ln2uk8, i32 %ln2uky, i32 ptrtoint (%templatezmhaskell_LanguageziHaskellziTHziSyntax_zdfDataFunDepzuzddData_closure_struct* @templatezmhaskell_LanguageziHaskellziTHziSyntax_zdfDataFunDepzuzddData_closure to i32), i32 %ln2ul2, i32 %ln2ul6, i32 %SpLim_Arg) nounwind Broken module found, compilation aborted! 0 libLLVM-3.0.so 0x4058f348 1 libLLVM-3.0.so 0x4058f7b4 2 libc.so.6 0x4150a0b0 __default_sa_restorer_v2 + 0 3 libc.so.6 0x41508c7c gsignal + 64 4 libc.so.6 0x4150a2bc abort + 432 5 libLLVM-3.0.so 0x406f88e0 6 libLLVM-3.0.so 0x406e7678 llvm::FPPassManager::runOnFunction(llvm::Function&) + 440 7 libLLVM-3.0.so 0x406e7760 llvm::FPPassManager::runOnModule(llvm::Module&) + 48 8 libLLVM-3.0.so 0x406e733c llvm::MPPassManager::runOnModule(llvm::Module&) + 396 9 libLLVM-3.0.so 0x406e7484 llvm::PassManagerImpl::run(llvm::Module&) + 108 10 opt 0x00014528 main + 2268 11 libc.so.6 0x414f2dd0 __libc_start_main + 272 Stack dump: 0. Program arguments: opt /tmp/ghc22413_0/ghc22413_0.ll -o /tmp/ghc22413_0/ghc22413_0.bc -O2 1. Running pass 'Function Pass Manager' on module '/tmp/ghc22413_0/ghc22413_0.ll'. 2. Running pass 'Module Verifier' on function '@seuH_info' make[1]: *** [libraries/template-haskell/dist-install/build/Language/Haskell/TH/Syntax.o] Error 1 (full log at http://arm.koji.fedoraproject.org/koji/getfile?taskID=746853&name=build.log, more details at http://arm.koji.fedoraproject.org/koji/taskinfo?taskID=746853) I haven't tried HEAD yet though the results at http://darcs.haskell.org/ghcBuilder/builders/kgardas-linux-arm-head/index.h… are not too encouraging. Perhaps I will try building ghc74 on ARM without llvm first, and maybe on Fedora 17 too? Anyway thoughts on how to proceed? Thanks, Jens ps There is actually a proposal to make ARM a Fedora 18 Primary Architecture - though personally I feel it is a bit too early yet - if that happens then this would become a more serious problem, though I know ARM is still not a Tier 1 ghc platform.

3 6

optimizer, spec-constr changes 7.2.2 -> 7.4
by Christian Höner zu Siederdissen 30 Apr '12

30 Apr '12

Hi, I am currently trying to get my ADPfusion library to optimize code using ghc-head (same thing described below happens with 7.4.1). Using ghc-7.2.2, both test programs (Nussinov78 and RNAFold) optimize well, the performance is close to C and ghc-core shows good code. This is mostly to say that optimization using ghc-7.2.2 is not an accident but works reliably. Unfortunately, with ghc-head it seems that constructor specialization does not happen. I see a lot of "case x of, Left -> ..., Right -> ..." and "case x of, Yield -> ..." which leads to really bad (slow) code. As there are some discussions going on regarding the optimizer not optimizing (like the ticks exhausted [1] one), are there other changes in the optimizer that could affect it? spec-constr-count / threshold, simplifier phases, simpl-tick-factor, no-liberate-case I have tried... Thanks, Christian PS: This is a ask-first-try-to-find-a-simple-example-later mail ;-) [1] http://hackage.haskell.org/trac/ghc/ticket/5539

1 0

default instance for IsString
by Greg Weber 25 Apr '12

25 Apr '12

I would like to default IsString to use the Text instance to avoid ambiguous type errors. I see defaulting capability is available for Num. Is there any way to do this for IsString? Thanks, Greg Weber

23 59

Re: default instance for IsString
by John Lato 25 Apr '12

25 Apr '12

> From: Yitzchak Gale <gale(a)sefer.org> > > Erik Hesselink wrote: >> I don't think IsString should be dismissed so easily. > > I'm just saying I don't want to be forced to use it. > If others like it, I'm not dismissing it. > >> we have a couple of newtypes over Text that do different kinds of >> normalization. An IsString instance for these is useful and total. > > True. Perhaps you'd be able to get IsBuiltinString instances > for those too, using newtype deriving, if only the method > names of IsBuiltinString are hidden and the class name is > exported. > > If that doesn't work, I'm fine with using a quasiquoter for > those instead. Or even just the usual newtype unwrapping > and wrapping. And again, if you provide IsString and others > want to use it, that's fine. I don't see how it would be possible to use a hidden IsBuiltinString as you describe without bringing Text into base (or alternatively not providing Text support). Perhaps unfortunately, I think that makes this solution a non-starter. I think a neater solution would be some sort of modular String typing, as I'm pretty sure somebody else on this list already mentioned. Perhaps a pragma like "DefaultString Data.Text.Text", which would mean that string literals would be treated as the provided monomorphic type, on a per-module basis? John Lato

1 0

Records in Haskell: Explicit Classy Records
by Matthew Farkas-Dyck 23 Apr '12

23 Apr '12

Hello GHC users. I made another proposal for records in Haskell, meant to solve just the namespace problem, and no more. http://hackage.haskell.org/trac/ghc/wiki/Records/ExplicitClassyRecords In this system, record selectors are overloaded in explicitly-user-declared type classes. Thus one can control the scope as of any other type class. Cheers, strake

3 2

Re: default instance for IsString
by Greg Weber 22 Apr '12

22 Apr '12

so how can I update the documentation? I asked some of the most experienced Haskell users at the Hackathon about this, and looked through any documentation I could find and there was nothing indicating I could do what you sent in your last message. On Sun, Apr 22, 2012 at 8:15 AM, Markus Läll <markus.l2ll(a)gmail.com> wrote: > The core of it is in the GHC docs' overloaded strings section [1]. > > It could be clearer though -- reading about defaulting in the reports, > in the type defaulting section of GHC docs and in [1] can be a bit > confusing. > > [1] http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensio… > > On Sun, Apr 22, 2012 at 4:54 PM, Greg Weber <greg(a)gregweber.info> wrote: >> Thanks Markus, I think you have saved the day! >> Even after googling for this extension and searching in the manual I >> am still coming up pretty blank. >> Is there somewhere I missed where this is documented or somewhere I >> can contribute documentation? >> >> On Sun, Apr 22, 2012 at 4:47 AM, Markus Läll <markus.l2ll(a)gmail.com> wrote: >>> ExtendedDefaultRules > > > > -- > Markus Läll

1 0

Finding/fixing stack overflow.
by David Brown 21 Apr '12

21 Apr '12

I've isolated the below small piece of code that is giving me a stack overflow. I'm kind of at a loss as has to fix, or even find what is happening here. (The real program is reading the data from a file, and doing something more complex with it). I'm not even sure how to work around this issue. It fails for me when given an argument of 1000000. Any ideas? I'm running 7.0.4, but I've tried this with ghc 6.12.3, and 7.4.1. Thanks, David ---------------------------------------------------------------------- import Control.Applicative import Control.Monad import Data.Binary import Data.Binary.Put import Data.Binary.Get import Data.List import Data.Word import System.Environment putValues :: [Int] -> Put putValues vals = mapM_ (putWord32le . fromIntegral) vals getValues :: Int -> Get [Int] getValues count = replicateM count (fromIntegral <$> getWord32le) goofySum :: Int -> Int goofySum count = let block = runPut $ putValues [1 .. count] in foldl' max 0 $ runGet (getValues count) block main :: IO () main = do args <- getArgs let count = case args of [c] -> read c _ -> error "Invalid usage" putStrLn $ show $ goofySum count ----------------------------------------------------------------------

2 1

Build failure with HEAD
by Austin Seipp 20 Apr '12

20 Apr '12

Hi, Building GHC HEAD (git HEAD SHA1 = 88f476b98709731d997ab57612cce4753cb65a0a) this morning, I've encountered 2 build failures that seem to be a result of some recent changes in the past day or two. If I build a clean repository with `make -j13` on my 12 core machine, I get: ------------------------------------------------------------------------------ compiler/hsSyn/Convert.lhs:178:30: `td_fvs' is not a (visible) field of constructor `TyData' compiler/hsSyn/Convert.lhs:190:31: `td_fvs' is not a (visible) field of constructor `TyData' make[1]: *** [compiler/stage2/build/Convert.o] Error 1 make[1]: *** Waiting for unfinished jobs.... --------------------------------------------------------------------------- However, reinvoking `make` with no parallelism and attempting to continue the build (there's no race condition obviously, I was just curious,) I get another (possibly related) build failure as well: --------------------------------------------------------------------------- compiler/deSugar/DsMeta.hs:326:18: Constructor `FamInstD' should have 2 arguments, but has been given 1 In the pattern: FamInstD fi_decl In the pattern: L loc (FamInstD fi_decl) In an equation for `repInstD': repInstD (L loc (FamInstD fi_decl)) = do { dec <- repFamInstD fi_decl; return (loc, dec) } make[1]: *** [compiler/stage2/build/DsMeta.o] Error 1 --------------------------------------------------------------------------- I would assume someone forgot to push something perhaps, but I figured naturally someone should be aware so they can fix it. :) -- Regards, Austin

1 0